Signal transmission system

ABSTRACT

629,174. Transparent cables for conveying light by internal reflection. MARCONI&#39;S WIRELESS TELEGRAPH CO., Ltd. Oct. 16, 1946, No. 30864. Convention date, Oct. 31, 1945. [Class 97 (i)] [Also in Group XL (b)] In a signal transmission system, electric signals from a plurality of sources are translated into modulated light signals of distinctive separable characteristics, which are transmitted through a light guide, emitted through a plurality of windows in the guide and illunuinate a plurality of photoelectrically-sensitive devices, each of which is selectively sensitive to a particular light signal, to produce an electrical output similar to the appropriate input signal. Fig. 1 shows a multichannel television distribution system wherein signals from antennµ 15, 16, 17 are demodulated by receivers 18, 19, 20, amplified, and the video signals are applied to modulate radiant energy sources 23, 29, 31 such as glow lamps, Kerr cells, or cathode-ray tubes. The modulated light passes through selective optical wavelength filters 41, 42, 43 to a light guide 36 consisting of a branched tube having a reflecting inner surface, or a rod of translucent or transparent material such as quartz or an acrylic or polystyrene resin. The light guide has windows 48, 49, 50, allowing the modulated light to pass through selective filters 61, 63, 69 corresponding with filters 41, 42, 43 and to illuminate photocells 58, 66, 73 feeding receivers 53, 54, 55, each comprising a video amplifier, a sync. separator, a deflection generator and a cathode-ray tube, to reproduce a picture corresponding to the signal received by the appropriate antenna. A light guide such as 62 may be interposed between window and photo-cell. In a modification (Fig. 2, not shown) the modulated light corresponding to a particular incoming signal is selectable by the interposition of one of a number of alternative filters between a light guide window and a photo-cell feeding a receiver and C.R. tube supplied with deflection voltages from a central source. Fig. 3 shows a device for transmission of sound or other intelligence wherein signals from a microphone or other source 96 are amplified and modulate the output of a light source 99 directed into a light guide 102 illuminating photo-cells 106, 107 through windows 103, 104. The photo-cell outputs are amplified and feed loudspeakers or other transducers 111, 112. In further modifications (Figs. 4, 5, not shown), electron multipliers replace the photo-cells, and cathode-ray tubes with different screen fluorescence colours replace glow lamps with optical filters.

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May 9, 1950 R. D. KELL lET AL. 2,506,672

SIGNAL TRANSMISSION SYSTEM 2 Sheets-Sheet 1 y Til-+1.

Filed Oct. 31. 1945 75 (sA/T2A; D fflft/O/V l' M 93 il. ATTORNEY May 9, 1950 R. D. KELL. ET Ax. 2,506,672

SIGNAL TRANSMISSION SYSTEM Filed- Oct. 5l, 1945' 2 Sheets-Sheet 2 96 9g //2 D6: u

T PIL 9 INVENTORS ,642/ C2-a.

WM? f ATTORNEY Patented May 9, 1950v ascesa rrlca SIGNAL TRANSMISSION SYSTEM Ray D. Kell and George C. Sziklai, Princeton, N. J.,

assignors to Radio Corporation of America, a

corporation of Delaware Application October 31, 1945, Serial No. 625,890

(Cl. Z50- 7) 2 Claims.

The present invention relates to signal transmission systems and more particularly, although not necessarily exclusively, to a guided-signal transmission -system for television signals and the like. y

In accordance with the present invention, there is provided an economical method and medium ior"transrnitting one or several signals, such as television signals, to several receiving points or stations by means of modulated light, and also, a simple method is provided for separating such signals.

The primary object of the invention is to provide a signal transmission system for simultaneously transmitting a plurality of signals with minimum attenuation and substantially without distortion. l

Another' object resides in the provision of a novel arrangement for combining signals for transmission and for separating the signals at a .receiving point or points.

A 'further object is to provide Vin a novel manner for selecting any one of' a plurality of transmitted signals.

A still further object is to provide a novel means for producing and utilizing signal modulated light.

A still further object is to provide a novel transmitter or conductor of light flux or other radiant energy including means for combining.

and separating light fluxes or other radiant en'- ergy introduced from a plurality of sources.

Other objects and 'advantages of the present invention willfof course, become apparent and immediately suggest themselves to those skilledv in the art to which the inventionis directed from a reading of the following specification in corrnection with the accompanying drawing in which:

Fig. l shows, schematically, a guided transl mission system for television signals in accordance with the invention;v

Fig. 2 illustrates a modification of the system of Fig. 1;

Fig. 3 shows the transmission system of the invention applied to thegtransmlssion of sound modulated signals; I

Fig. 4 illustrates a further modification of the system of Fig. 1;'and

Fig. 5 shows a novel arrangement in accordance with ythe invention for obtaining' signal modulated light flux.

Referring to Fig. l, a three channel system for the distribution of television signals is shown. A television signal includes extremely high and extremely low frequency components as well as portions having steep wave-fronts, and therefore. a television signal requires special transmission channels for transmission even over short disposes, no effect on the transmitted signal frequencies. That is to say, there is absorption of the light iiux or radiant energy carrier, but this absorption does not vary appreciably with the modulating frequency.

The television signals are received by UHF (ultra high frequency) radio transmission through antennas I5, I6, and Il, connected or coupled to television receiversI IB, I 9, and 20, respectively. Each antenna, being tuned to the signal to be received and having the proper directivity with respect to the modulatedl signal transmitting source, will provide an optimum signal. The receivers i8 to 20 may be of any type suitable for the purpose and may include the usual means for demodulating the UHF signal so as to obtain the video signal therefrom.

The video signal from each receiver, for ex ample the video signal from receiver i8, is applied in any suitable manner to modulate a radiant energy source or a light source such, for example, as a glow tube 23. For example, the signal from the receiver I8 may be supplied to an amplifier 24 or other apparatus suitable fox' modulating the device, such as the lamp 23, which provides the modulated light flux or modulated radiant energy to be introduced into the light conducting means of the invention indicated generally by reference character 26. The glow' lamps or other light or radiant energy sources 29 and 3i, respectively, are connected to the rcceivers i9 and 20, respectively, through devices 33 which are or may be similar to the device 2G.

Although glow lamps have been shown for the sake of convenience of illustration, it will be understood that each light source fed by the radio receivers may be a Kerr cell of the Karolus type, for instance, a cathode ray tube with a low persistence screen, or the like. Kerr cell of the Karolus type is shown in United States Patent No. 1,885,604, granted to A. Karolus November l, 1932. Fig. 5, later to be described, is illustrative of the cathode ray activated type of light` source.

The light conducting means 26, in accordance An example of a asoae'ze with the invention, may be in the form of a rod invisible portion of the spectrum may be employed if desired.

Where the plastic rod is roughened in somev mazmer, as by sanding, some of the guided light will escape, or in other words, the modulated light will appear at the surface. In front of this sanded surface or window, a sensitive photocell, for example, or other device responsive to light, will convert the light modulation to 4an electric current having the same modulation as that of the original signals. By placing a filter between the sanded surface and the photocell, any one of the signals may be selected. For example, in

Fig. 1, sanded surfaces or windows are indicated at 48, 49, and 50. A plurality of receivers indi- -cated generally by reference characters 53, 54,

and 55, are shown, and any receiver may be made responsive to any one of the signals provided by the radio receivers I8 to 20, depending on the kind of light filter placed between the photocell and thc window on the rod 36. For example, the photocell 58, associated wtih the receiver 53 may operate in accordance with signals from the radio receiver |8 if the filter 6| is similar to the filter 4I. An additional light conducting rod may, if desired,'be interposed between a window on the rol 36 and a photocell. A light filter may be positioned before the window in the main rod,

' v or'beiore the photocell. The latter arrangement is shown in Fig. 1 wherein la rod 92 serves as an auxiliary link. The .filter 63, interposed between the window 49 and the photocell 66, may be similar to the filter 42, and lter 69, interposed between the window 50 and the photocell 13, may be similar to the filter 43. With the suggested arrangement substantially complete separation of the signals present in the modulated light flux is obtained.

The receivers 53 to 55 are or may be similar and may be constructed and operated in known manner. A description of the receiver 53 will suffice for all three.

The signal current in the output of the photocell 58 has the same modulation as the carrier signal received by the receiver l0 with the aid of the antenna I5. That is to say, the demodulated signal from the amplifier and modulator 24 which yactuates the glow tube 23v is the same as the electrical signal appearing in the output of the photocell 58. This signal may, as stated above, include the video signal accompanied by the sync signals and is applied to a video amplifier 76 and a sync signal separator 78. Signal separation is accomplished in the sync signal separator i8, and control signals are supplied from this separator to a deection generator v0|. An example of a sync signal separator is shown in United States Patent to Bedford, No. 2,207,775, granted July 16, 1940. Horizontal and vertical sweep frequencies of appropriate waveform are applied to the deflection system of an image producing device, such as a iiuorescent screen or target cathode ray tube 82. The video signals are suppiled to the tube 82 from the output circuit of reproduced by transducers and |,|2.

the previously mentioned video amplifier 1. Similarly, images appropriate to the signal selection of the lters 63 and 69 are produced by the cathode ray tubes 83 and 84. In the example shown, tubes 83 and 84 will exhibit images corresponding to signals from radio receivers I9 and 20. The manner in which this is accomplished in accord-ance with the invention will, it is believed, be obvious in view of the foregoing.

Fig. 2 of the drawings illustrates a modification of the system of Fig. 1 in which a receiver designated 86 may be used for producing images on itsassociated cathode ray tube 88 so that an image represented by signals received by any one of the radio receivers may be reproduced. A

4section of a signal guiding means, such as 26 in Fig. 1, is designated 36a, and a series of filter sections 38, 39, and 40 are retained in any suitable manner so that any one of these filter sections may be selected to be interposed betweenA the window 50a and a photocell 9|. As a further modification of the system of Fig. 1, the ray deecting means for the tube 88 may be produced by a deflection generator 92 operating under control of a separate source of deflection control signals furnished over a connection 93.

Fig. 3 of the drawings illustrates an arrangement whereby the method of communication of the invention may be usedfor distribution of sound orother intelligence. A signal generator, such as a microphone 96 and an amplifier 98,01 any other signal source, modulates the light output of a light source such as a glow tube 99. Other light sources mentioned herein may also be used for the purpose. The light from thelight source 99 is directed into a guiding rod |02 which is provided with windows |03 and |04. The window |03 may be provided in the manner previously described. Photocells |06 and |01 convert the light modulation into an electric signal which is amplified by the amplifiers |08 and |09 and These transducers may be loudspeakers, phones, etc.

Fig. 4 of the drawings illustrates the use of an lelectron multiplier photocell which may be used to advantage. A high potential power supply I4 is usually presentsince itis needed for operation of certain types of cathode ray reproducing tubes. Where the vtube llt` is of this type high voltage from the power supply is therefore readily available for operation of an electron multiplier photocell |8 shown conventionally. The photocell may be similar to that disclosed in U. S. Patent No. 2,219,871, granted October 29, 1940, to Louis Malter. High voltage is applied to the collector electrode of the photocell over a connection |20, and signals amplified 4by the multiplier action of the photocell are transferred by a condenser` |22 to the control electrode |24 of the cathode ray tube H6. The signals are also applied to a sync signal separator and deflection control unit |26 of any well known form. A portion of a light guiding or conducting means is designated 36h, and an appropriate iilter |28 is interposed between a window |29 on the light guide 36h and the light sensitive section of the photocell ||8.

Fig. 5 of the drawings shows illustratively anl arrangement employing a beam modulated cathode ray tube as a light source. Diierent colored phosphor-s may be used, and the filters may be eliminated. For example, phosphors of zinc oxide family generally have a fraction of a microsecond delay time and may be used advantageously.

In Fig. 5, |8a and |9a are radio receivers fedv from antennas |5a and wa, respectively. Ampliers and demodulators 24a and 33a supply amplified and demodulated signals to the control grids |32 and |33 of cathode ray tubes |36 and |31. Each of the tubes |33 and |36 is provided with an electron gun arrangement |39, and the beam produced by this gun is modulated by the control grid of the tube. The target area |4| of each tube may be coated with an appropriate phosphor. and the light produced by bombardment is picked up by the branches |43 and |44 of a light guiding rod 36a. The cathode ray beam ".1 each of the tubes |36 and |3`| need'not be sharply focused, thereby making it possible to obtain a suiiicient quantity of light flux without-'damage to the fluorescent material.

Having now described the invention, what is claimed and desired to be secured by Letters Patent is the following:

1. A signal transmission system comprising a.

light guide of light transmitting material, a plu' rality of means for producing signal modulated light for transmission through said light guide, each of said means producing light of a different color, a plurality of windows in said light guide each window designed to emit at least a portion of the total signal modulated light being transmitted, a plurality of photocells, each cell being positioned to receive light directed from one of said windows, means interposed between each window and its associated photocell to serve as a color filter, a signal translating device for each photocell, and signal amplifying means interconnecting each photocell with its associated signal translating means.

2. A signal transmission system comprising a light guide of light transmitting material, a plurality of means for producing signal modulated light for transmission through said light guide, a plurality of light filter means one associated with each source of signal modulated light whereby to admit light of a single color to said light guide, a plurality of windows in said light guide, each window designed to emit at least a portion of the total signal modulated light being transmitted, a plurality of photocells, each cell being positioned to receive light directed from one of said windows, means interposed between each window and its associated photocell to serve as a color filter, a'signal translating devicev for each photocell,

and signal amplifying means interconnecting each photocell with its associated signal translating means.

RAY D. KELL. GEORGE C. SZIKLAI.

REFERENCES CITED le of this patent:

UNITED STATES PATENTS Number Name Date 1,919,888 y Hough July 25, 1933 1,981,999 French Nov. 27, 1934 2,070,418 Beverage Feb. 9, 1937 2,071,284 Hyland Feb. 16, 1937 2,100,348 Nicolson Nov. 30, 1937 2,187,908 McCreary Jan. 23, 1940 

